SHAPE CHANGE OF SURFACE CRACKS IN ROUND BARS UNDER CYCLIC AXIAL LOADING

An elliptical-arc surface crack in a round bar under cyclic axial loading with constant amplitude is considered. The stress-intensity factor along the crack front is calculated through a finite-element analysis by employing isoparametric solid elements. Then the fatigue crack propagation is examined by means of the Paris-Erdogan law. The aspect ratio a/b of the initial flaw is made to vary from 0.0 (straight crack front) to 1.0 (circular-arc crack front). Moreover, different material properties and loading parameters are considered. For each case being analysed, it is shown that the surface cracks tend to follow preferred propagation paths, with the flaw aspect ratio converging to a value in the range 0.6-0.7.